Meanwhile, the New York Times reports that former Trump aide Michael Flynn told his transition team at the beginning of January – earlier than was previously thought – that he was under federal investigation for working as a paid lobbyist for Turkey during the election campaign.

Mr Trump appointed Mr Flynn as his national security adviser weeks later despite the warning, but he was sacked after just 24 days.

Image copyrightAFP

Image caption
Mr Flynn was sacked for misleading the vice-president about his contacts with Russian officials

In his statement announcing Mr Mueller’s appointment, Mr Rosenstein said: “The public interest requires me to place this investigation under the authority of a person who exercises a degree of independence from the normal chain of command.”

Mr Mueller, who will have wide-ranging powers, said simply: “I accept this responsibility and will discharge it to the best of my ability.”

Just over an hour after the news of Mr Mueller’s appointment emerged, President Trump predicted the new investigation would clear him and his team.

“A thorough investigation will confirm what we already know – there was no collusion between my campaign and any foreign entity,” said the president.

In announcing the appointment of a special counsel, Mr Rosenstein cited the “unusual circumstances” of the ongoing FBI Russia investigation. That’s an understatement.

The circumstances are not just unusual, they are unprecedented. The nation has never had an administration so embattled so early in its term. There have never been such grave allegations of electoral meddling by a foreign power in a US presidential election.

Then again there has never been a president quite like Donald Trump.

Now the Russia story enters a new, more serious phase. Robert Mueller has a sterling reputation in Washington, DC. He worked with Mr Comey when the latter served as deputy attorney general in George W Bush’s administration. He understands pressure-cooker politics and knows how to navigate the corridors of power.

He has wide latitude to conduct his investigation and bring criminal charges, if necessary.

While Mr Mueller is technically still part of the justice department and ultimately reports to Mr Trump, his stature is such that he is unlikely to be cowed by the president.

Independent investigations often take on a life of their own and can reach unexpected conclusions. With Mr Mueller in the game, the stakes just went up.